The morning after a handful of N.F.L. players renewed their protests against social inequality and police brutality by raising fists or kneeling during the playing of the national anthem, President Trump renewed his criticism of their actions.

The N.F.L.’s 2018 preseason began in earnest on Thursday with the first full slate of games, and the question that has dogged the league all summer — will players continue social justice protests during the playing of the national anthem — was answered loud and clear.

Malcolm Jenkins of the Philadelphia Eagles, one of the most outspoken players in recent years, was joined by his teammate De’Vante Bausby in raising a fist while the anthem was played. As had been customary in the past, Chris Long, a veteran defensive end, stood next to Jenkins with a hand on the defensive back’s shoulder.

In the only reported instance of players kneeling, Kenny Stills and Albert Wilson of the Miami Dolphins took a knee during the anthem before their team’s game against the Tampa Bay Buccaneers, while their teammate Robert Quinn raised his fist.

President Trump, who has been vocal in his opposition to using the anthem as a stage for protest, responded on Friday morning with a pair of tweets blasting Jenkins, Stills and others who didn’t stand at attention.

Stills and Wilson, though, received praise on social media from Colin Kaepernick, the inactive player whose protests as a member of the San Francisco 49ers started this movement.

Stills told reporters after the game that he and Wilson had not coordinated a demonstration in advance of the game.

“It just happened that way,” Stills said. “When I’m on a knee, most of the time I’m praying, and thank God for having Albert next to me. Being a part of this protest hasn’t been easy. I thought I was going to be by myself out there. Today I had an angel with me with Albert being out there. I’m grateful he sees what’s happening, and he wants to do something about it as well.”

Elsewhere, four members of the Jacksonville Jaguars (Telvin Smith, Jalen Ramsey, Leonard Fournette and T.J. Yeldon) waited in the tunnel until after the anthem had concluded before their team’s game against the New Orleans Saints, and three members of the Seattle Seahawks (Quinton Jefferson, Branden Jackson and Duane Brown) did the same before their team’s game against the Indianapolis Colts.

In a notable shift, however, the 49ers, who had been one of the more active political teams in previous years, did not appear to have any players kneeling during the anthem before their game against the Dallas Cowboys. Marquise Goodwin, a wide receiver, had his right arm raised for the duration of the song.

For Jenkins, who had stopped demonstrating last season after he and a coalition of players secured increased financing for social issues from the league, the preseason game represented a return to his old form. In addition to raising his fist, Jenkins and some of his teammates on the defending champion Eagles took the field for warm-ups wearing T-shirts highlighting various statistics about racial disparities in prisons.

That Jenkins went back to demonstrating was not surprising after his strong reaction to recent changes in the league policy regarding behavior during the anthem.

“Quite frankly, guys in our league don’t like being told what to do, what they can and can’t do,” Jenkins told Philly.com. “We don’t have this type of policies for the other causes we support, whether it be our ‘Salute to Service,’ or breast cancer awareness, or anything else. It’s just when you start talking about black folks, quite frankly. It’s disheartening, but we’ll continue to be creative.”

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Robert Quinn of the Miami Dolphins raised his fist during the playing of the national anthem on Thursday. Two of his teammates knelt while the song played.CreditWilfredo Lee/Associated Press

The protests came less than three months after the league, without consulting the players’ union, updated its rules to obligate players to stand on the field during the national anthem, or remain in the locker room. Previously, players were obligated to be on the field but were only encouraged to stand.

Over the past two seasons, dozens of players across the league protested during the anthem to raise awareness of social injustice and police brutality against black people. The protests turned into a full-blown crisis for the league last September when President Trump criticized the league’s owners for not penalizing players who protest.

In response to backlash from the president and some fans, the league tightened its policy, which now includes potential fines against teams whose players protest. The league has allowed teams to decide on their own whether they want to penalize players directly.

It is unclear whether the protests on Thursday will continue in the weeks ahead. Some players may have just wanted to show their displeasure with the new policy, while others may have wanted to stand up to President Trump.

No players protested when the N.F.L. kicked off its 2018 season last week when the Baltimore Ravens and the Chicago Bears played in the Hall of Fame Game in Canton, Ohio.

Over the summer, players across the league have said they are opposed to the league’s new policy. Some players, most notably defensive tackle Jurrell Casey of the Tennessee Titans, said they would continue to protest and pay any fines if necessary.

At the same time, teams issued their own proclamations. Last month, Dallas Cowboys owner Jerry Jones said that he expected everyone on his team to stand for the anthem and not stay in the locker room. His son Stephen added that players who did not follow the team’s directive would be cut.

Cornerback Richard Sherman of the San Francisco 49ers accused Jerry Jones of having a “plantation mentality.”

Other owners have been more conciliatory. Jed York, whose family owns the San Francisco 49ers, abstained from voting on the new policy. Chris Johnson, the acting owner of the Jets, said players who protested would not be penalized.

In Florida, the Miami Dolphins head coach Adam Gase said he would not discuss the anthem issue with his players and does not want to be caught between the owners’ rules and the players.

“I’m coaching football,” he told The Palm Beach Post. “I’m not dealing with all of this.”

The players who protested on Thursday may not be penalized. After the N.F.L. Players Association filed a grievance in July arguing that the new policy violated the N.F.L.’s collective bargaining agreement, the league agreed to freeze the enforcement of the policy while it tries to work out a potential solution with the union.

Meanwhile, Kaepernick, the player who was the first to protest in 2016, has not returned to the N.F.L. He filed a grievance against the league, accusing the owners of conspiring to keep him out of job.

The league appears to be going to great lengths to tamp down any hint of protest. According to Pro Football Talk, Electronic Arts, which makes the Madden video game, deleted Kaepernick’s name, along with various profanities, from the song “Big Bank” by YG, which serves as a soundtrack to the video game. Electronic Arts later claimed the deletion was a miscommunication about the company’s ability to reproduce Kaepernick’s likeness in the game, and the company vowed to restore the references to his name.

Eric Reid, Kaepernick’s teammate on the 49ers who also regularly knelt during the playing of the national anthem in 2016 and 2017, is also unsigned. He, too, has filed a grievance against the league.

A version of this article appears in print on , on Page B9 of the New York edition with the headline: N.F.L. Players Resume Anthem Protests. Order Reprints | Today’s Paper | Subscribe